Achromatic chicanes are frequently used in accelerators and beam lines to avoid mechanical interferences amongst components, provide adjustment of beam path length and time of flight, and to introduce momentum compaction for management of the beam longitudinal phase space. The geometry of a conventional chicane (see FIG. 1 described more fully below) illustrates that all of these functions are linked. The geometry is set by the chicane excitation, as is the path length and the momentum compaction. It is not possible to change one property without altering the other two. Moreover, the accessible range of path length variation and momentum compaction is limited by the available bend fields and/or bend aperture and/or range of motion of the central bend. Finally, it is not possible to make such a chicane linearly isochronous without the introduction of external focussing elements between the dipoles/magnets so as to provide a modulation of off-momentum orbits to make their path length or time of flight identical to that of the on-momentum orbit. Management of higher order momentum compactions is even more difficult; the introduction of external focussing elements imposes asymmetries on the system that render it generally unobvious as to where to appropriately locate the required nonlinear correction elements.
It would therefore be highly useful to have an achromatic recirculated chicane of a fixed geometry that provides independently variable path length and independently controllable momentum compaction.